Diabetic retinopathy is a major cause of blindness in the United States. Increased expression of inflammatory molecules and death of retinal endothelial cells (capillary degeneration) with resulting local retinal ischemia are believed to be important for development of this disease. We uncovered CD40 as a major driver of the upregulation of inflammatory molecules in the retina and development of capillary degeneration in experimental diabetic retinopathy. In addition, CD40 in Mller cells triggers purinergic signaling (ATP-P2X7) that drives expression of pro-inflammatory cytokines in by-stander microglia/macrophages and programmed cell death of retinal endothelial cells. [VEGF upregulation is an event central to capillary leakage and retinal neovascularization in diabetic retinopathy. VEGF upregulation in the diabetic retina is driven by activation of the Unfolded Protein Response (UPR) in Mller cells. However, we have an incomplete understanding on how UPR is activated in the disease.] The objective of this application is to further our understanding of the [induction of UPR, the upregulation of VEGF] and inflammatory molecules in diabetic retinopathy. The central hypothesis is that a specific signaling pathway downstream of CD40 controls [UPR, VEGF upregulation and the ATP-P2X7 cascade such that selective blockade of this pathway will prevent UPR, VEGF upregulation,] inflammatory molecule upregulation, capillary degeneration and will protect against experimental diabetic retinopathy. [In the first aim we will examine how CD40 stimulates UPR in Mller cells. In the second aim we will determine if CD40 upregulates VEGF via UPR and whether the signaling pathway that mediates UPR/VEGF upregulation is different from the pathway that causes direct upregulation of inflammatory molecules in Mller cells. Both aims will be pursued using genetic approaches that block specific signaling pathways.] In the third aim we will use an animal model of experimental diabetic retinopathy and transgenic mice to determine if [CD40 drives UPR and VEGF upregulation in vivo and whether genetic blockade of an upstream event in CD40 signaling impairs upregulation of UPR, VEGF and various inflammatory molecules in the diabetic retina.] Using similar methodologies, in the fourth aim we will test the in vivo effects of a specific inhibitor of CD40 signaling in the induction of the events described above. [The proposed work will further our understanding of UPR/VEGF upregulation in diabetic retinopathy] and may lead to further development of selective inhibitors of CD40 signaling as a novel approach for treatment of diabetic retinopathy.